Changeset 679:9c7639f3a741 in lemon-1.2 for cmake

Minor CMake improvements

• Use the empty ELSE(), ENDIF(), ENDMACRO(), etc. syntax since this improves readability and requires less typing.
• Use FIND_PACKAGE() instead of INCLUDE().
• Use the value of CMAKE_COMMAND variable instead of cmake, since this works even if cmake is not in the PATH.